The present invention relates to a magnetic card and apparatus for reading data from the magnetic card, apparatus for recording data on the magnetic card and apparatus for both.
Magnetic cards are becoming common as credit cards, pre-paid cards etc. because of their cost efficiency and their compactness compared to the amount of data they can bear. Conventional magnetic cards comprise a card body usually made of plastics, a magnetic layer laid on the plastic card body and a protection layer laid on the magnetic layer for a physical protection thereof. Because data recorded on this kind of conventional magnetic cards can be read by using conventional magnetic card readers and recorders, they are open to surreptitious reading, recording and modification.
One solution for laying ban on the above-mentioned surreptitious access to the card is to form a plurality of magnetic layers on a card body, one layer overlaid by the other, and to protect the data by making it a rule to follow a prescribed procedure when accessing to the data. An example of this type of data protection is disclosed by Japanese Patent Application No. 40-23745 (D1) which is briefly described as follows.
According to D1, a first magnetic layer comprising a first magnetic material is formed on the card body and a second magnetic layer comprising a second magnetic material is formed on the first layer wherein coercive force of the first magnetic material is higher than that of the second magnetic material. When recording data on the card, magnetic field enough extensive to record data on the first magnetic layer is applied. Consequently, the data is recorded also on the second magnetic layer. In order to protect the data from surreptitious reading, a random magnetic field is applied to magnetize the second magnetic layer. Intensity of the random magnetic field is so determined as to prevent magnetization of the first magnetic layer. As a result, meaningful data is contained only in the first magnetic layer while the second magnetic layer contains random data. Therefore, by an ordinary reading means wherein a reading head comes in contact with the second magnetic layer from outside, the random data recorded on the second magnetic layer is read, consequently protecting the meaningful data written in the first magnetic layer from being read surreptitiously. In order to read the meaningful data, the second magnetic layer is first erased by applying a DC magnetic field. Then, the meaningful data in the first magnetic layer becomes accessible through the second magnetic layer.
A problem as to the above-mentioned magnetic card is that the second magnetic layer, even though the random data is erased, develops a spacing loss decreasing resolution of data recorded on the first magnetic layer and causing errors in reading them.
Another problem resides in that a relatively intensive magnetic field have to be applied to the first magnetic layer when recording data thereon, because it has high coercive force, resulting inevitably in an increase of cost for apparatus for reading and recording data on the magnetic card.